1. Field of the Invention
The present invention is directed to the field of cooling fans, particularly those of the type used with air conditioning condensers and radiators in automobiles and other types of vehicles.
2. Description of Related Art
In an air conditioning or other type of refrigeration system, a condenser is used to eliminate waste heat generated from the cooling process. A basic air conditioning system includes a compressor and an expansion valve. A condenser is typically a coiled arrangement of tubes, downstream of a refrigerant compressor and upstream of an expansion valve. An evaporator is a similar coiled arrangement of tubes, downstream of the expansion valve and upstream of the compressor. The condenser and evaporator are in fluid connection, and contain a refrigerant, which is a highly volatile liquid, i.e. a liquid having a very low specific heat of evaporation.
As refrigerant pressure is built up in the condenser, heat is produced, as is understood from the Idea Gas Law. Preferably, the condenser is cooled down as close as possible to ambient temperature. Upon throttling through the expansion valve, preferably a venturi or the like, the refrigerant expands into the evaporator, thereby cooling down, as is also understood from the Ideal Gas Law. Air is cooled by passing over the evaporator, resulting in refrigeration or air conditioning.
In order to efficiently eliminate the heat produced in the condenser, it is typical to use a fan to induce a flow of ambient temperature air over the condenser coils, so as to increase the rate of heat transfer from the coils to the ambient temperature. In a common vehicle design, the condenser is mounted next to the radiator of the engine cooling system, and a common condenser/radiator fan is used, electrically powered by the vehicle's alternator. However, the condenser/radiator fan is typically located in the front of the vehicle, in the path of the air flow produced by the vehicle's forward motion. As a result, this air flow is also in contact with the condenser, thereby producing an air flow cooling effect in addition to the cooling produced by the fan. This effect varies with the speed of the vehicle. At low vehicle speeds, the air flow cooling makes a small contribution. As vehicle speed increases, the air flow cooling effect is greater. At high speeds, under certain environmental conditions, the air flow cooling alone is sufficient to produce the required condenser cooling, thereby making the fan superfluous. However, in a typical vehicle air conditioning system, the condenser/radiator fan is designed to operate continuously with the operation of the air conditioning system. This places an additional load on the alternator's electrical output, which translates directly into the load on the vehicle's engine. So the fan's operation directly reduces the overall fuel efficiency of the vehicle.
Several factors influence the load placed on the condenser, and thus the efficiency of the air flow cooling effect as related to the operation of the condenser/radiator fan system. For example, the air conditioning load may vary in accordance with ambient temperature, solar load, relative humidity, vehicle speed and the user set point for the air conditioning system. Also, air flow cooling of the condenser can be influenced by the same environmental conditions. Further, these conditions can vary with variations in the weather, and even with varying traffic conditions, as vehicle speed changes. Thus, there has heretofore been no option but to continue to allow the condenser/radiator fan to continuously operate with the air conditioning system.
Therefore, there exists a need in the art for a method and system to control the condenser/radiator fan operation in response to operating conditions of the vehicle.